Instructions

Below you will find several empty R code scripts and answer prompts. Your task is to fill in the required code snippets and answer the corresponding questions.

Cereal Data

Today, we start by looking at a collection of breakfast cereals:

With variables:

Produce a histogram of the sugar variable.

Now, compute the standard deviation of the variable sugar:

## [1] 4.378656

What are the units of this measurement?

Answer: g^2

Now, compute the deciles of the variable score:

##   0%  10%  20%  30%  40%  50%  60%  70%  80%  90% 100% 
## 18.0 28.0 31.0 34.5 37.0 40.0 42.0 48.0 53.0 58.0 84.0

What is the value of the 30th percentile. Describe what this means in words:

Answer: 30% percent of the cereal has the health score below 34.5

Produce a boxplot of score and brand.

Which brand seems to have the healthiest cereals?

Answer: Nabisco has the healthiest cereals.

Produce a boxplot of score and shelf.

Produce a boxplot of sugar and shelf.

If I want a healthy but reasonably sweet cereal which shelf would be the best to look on?

Answer: You should look at the top shelf. According to the graph, the top shelf has a very high health score and the second high sugar amount in them.

Tea Reviews

Next, we will take another look at a dataset of tea reviews that I used in a previous lecture:

With variables: - name: the full name of the tea - type: the type of tea. One of: - black - chai - decaf - flavors - green - herbal - masters - matcha - oolong - pu_erh - rooibos - white - score: user rated score; from 0 to 100 - price: estimated price of one cup of tea - num_reviews: total number of online reviews

Draw a scatterplot with num_reviews (x-axis) against score (y-axis) and add a regression line (recall: geom_smooth(method="lm")).

Does the score tend to increase, decrease, or remain the same as the number of reviews increases?

Answer: Increase.

Calculate the ventiles of the variable price.

##     0%     5%    10%    15%    20%    25%    30%    35%    40%    45% 
##   8.00  10.00  10.00  10.00  10.00  10.00  12.00  12.00  12.00  12.00 
##    50%    55%    60%    65%    70%    75%    80%    85%    90%    95% 
##  13.00  15.00  15.00  17.00  19.00  20.00  30.00  35.35  49.30  86.75 
##   100% 
## 196.00

What is the 80th percentile? Describe it in words, include the units of the problem in your answer.

Answer: 80% of tea has price below 30 dollars.

Plot the number of reviews (x-axis) against the score variable. Color the points according to price binned into 5 buckets.

What tends to be true about the number of reviews for the most expensive 20% of teas?

Answer: They usually has less reviews since most of the purple dots (represented by the above 30 dollars expensive teas.) The score also varies from low to high.

Create a dataset named white that consists of only white teas.

Calculate the standard deviation of the price for white teas and the standard deviation of the price for all of the teas.

## [1] 13.59444
## [1] 30.42485

Is the variation of the white tea prices smaller, larger, or about the same as the entire dataset?

Answer: The variation of the white tea prices smaller than the price of all teas.

Summarize the dataset by the type of tea and save the results as a variable named tea_type.

Plot the average price (x-axis) against the average score (y-axis) of each type of tea. Make the size of the points proportional to the number of teas in each category and label the points with geom_text_repel and the tea type.

Describe an interesting pattern or set of outliers that you found in the previous plot. This does not need to take more than 1-2 sentences.

Answer: The matcha has a high price and a low score while others have a low price and a relatively higher score.